The present invention relates to a method and a device for controlling an internal combustion engine.
A method and a device for controlling an internal combustion engine are discussed in the German Published Patent Application No. 40 32 451. A sensor may be used for detecting a pressure variable that may characterize the pressure of the air supplied to the internal combustion engine. The performance reliability of the sensor may be monitored and a substitute signal may be used in case of a fault. If a fault is present, the output signal of a second sensor may be used as a substitute value. This method may require an additional sensor.
By using a static substitute value based on quantities characterizing the operating state of the internal combustion engine in determining the substitute signal, a substitute value may be provided in a simple and cost-effective manner. The static substitute value, defined for generating the substitute signal, may be filtered by a filter having a delay component. As a result of such filtering, dynamic effects may be taken into account. For instance, the charge-air pressure may have a delayed reaction in response to a change in the fuel quantity and/or rotational speed. Therefore, a precise simulation may only be provided if the output variable of the simulation has a delayed change in response to a change in the input variables.
A further improvement in the simulation may result if the response characteristic of the filter is specifiable as a function of operating characteristics.
The rotational speed of the internal combustion engine and/or the time derivative of the pressure variable may be suitable in this context. At different speeds, different time constants may be selected for the filter. Correspondingly, different time constants may be selected at rising and falling speeds. In this manner, the simulation may be more precisely adapted to the actual behavior of the signal.
A fault of the sensor may be recognized when a change in a variable characterizing the fuel quantity to be injected does not result in a change in the signal. In this manner, a reliable and simple fault detection may be made provided.